An intermediate transfer method color printer that is currently widely distributed as an image forming apparatus automatically conducts concentration detection and color shift detection every elapse of a constant duration or every certain print pages, and conducts correction based on detection results. However, correction for the concentration detection and the color shift detection needs time. Therefore, performance of the next printing is not allowed during the correction, which generates an inconvenience.
To solve such an inconvenience, an image forming apparatus disclosed in Japanese Laid-Open Patent Application No. 2008-164656 has been proposed, for example. The image forming apparatus uses a reading sensor (concentration sensor), which moves in a shift direction of a roller, to read an toner image so that performance time for a detection operation is shortened (For example, see Japanese Laid-Open Patent Application No. 2008-164656).
However, there is a problem in the above-discussed image forming apparatus disclosed in Japanese Laid-Open Patent Application No. 2008-164656 that reading the toner image formed by the reference image needs time when movement speed of the reference image detection unit and/or the reading sensor is slow since the reference image detection unit for detecting the reference image and the reading sensor move. Therefore, there are only small effects with respect to shortening the time needed for the reference image detection.
One of objects of the present invention is to solve such a problem.